Methods to Assess Beta Cell Death Mediated by Cytotoxic T Lymphocytes
Summary
Cell-mediated lymphocytotoxicity (CML) assays can be used to test autoreactive responses and study mechanisms of cell death in vitro. However, using live-cell confocal microscopic imaging techniques with fluorescent dyes, the type and kinetics of cell death as well as the pathways utilized can be studied in greater detail.
Abstract
Type 1 diabetes (T1D) is a T cell mediated autoimmune disease. During the pathogenesis, patients become progressively more insulinopenic as insulin production is lost, presumably this results from the destruction of pancreatic beta cells by T cells. Understanding the mechanisms of beta cell death during the development of T1D will provide insights to generate an effective cure for this disease. Cell-mediated lymphocytotoxicity (CML) assays have historically used the radionuclide Chromium 51 (51Cr) to label target cells. These targets are then exposed to effector cells and the release of 51Cr from target cells is read as an indication of lymphocyte-mediated cell death. Inhibitors of cell death result in decreased release of 51Cr.
As effector cells, we used an activated autoreactive clonal population of CD8+ Cytotoxic T lymphocytes (CTL) isolated from a mouse stock transgenic for both the alpha and beta chains of the AI4 T cell receptor (TCR). Activated AI4 T cells were co-cultured with 51Cr labeled target NIT cells for 16 hours, release of 51Cr was recorded to calculate specific lysis
Mitochondria participate in many important physiological events, such as energy production, regulation of signaling transduction, and apoptosis. The study of beta cell mitochondrial functional changes during the development of T1D is a novel area of research. Using the mitochondrial membrane potential dye Tetramethyl Rhodamine Methyl Ester (TMRM) and confocal microscopic live cell imaging, we monitored mitochondrial membrane potential over time in the beta cell line NIT-1. For imaging studies, effector AI4 T cells were labeled with the fluorescent nuclear staining dye Picogreen. NIT-1 cells and T cells were co-cultured in chambered coverglass and mounted on the microscope stage equipped with a live cell chamber, controlled at 37°C, with 5% CO2, and humidified. During these experiments images were taken of each cluster every 3 minutes for 400 minutes.
Over a course of 400 minutes, we observed the dissipation of mitochondrial membrane potential in NIT-1 cell clusters where AI4 T cells were attached. In the simultaneous control experiment where NIT-1 cells were co-cultured with MHC mis-matched human lymphocyte Jurkat cells, mitochondrial membrane potential remained intact. This technique can be used to observe real-time changes in mitochondrial membrane potential in cells under attack of cytotoxic lymphocytes, cytokines, or other cytotoxic reagents.
Protocol
Discussion
Cytotoxic T cell mediated beta cell death is the main pathophysiology of T1D 5. CML assays using 51Cr release allow us to study the degree of effector-target response 6. However, the detailed process and pathways of T cell-mediated beta cell death is still not fully understood. Since mitochondria are critical for beta cell function and death7, we focused on mitochondrial changes during the visual CML. Mitochondrial membrane potential dissipation is an early and irreversible…
Declarações
The authors have nothing to disclose.
Acknowledgements
This work was supported by grants from the National Institutes of Health DK074656 and AI56374 (CEM), as well as the Juvenile Diabetes Research Foundation.
Materials
| Name of the reagent | Company | Catalogue number | Comments (optional) |
|---|---|---|---|
| Cr-51 | Perkin Elmer | NEZ030500IMC | |
| PBS | Cellgro | 21-040-60 | |
| Tetramethyl Rhodamine Methyl Ester (TMRM) | Invitrogen | T668 | |
| Picogreen | Invitrogen | P7581 | |
| AI4 mimotope | mimotopes.com | amino acid sequence: YFIENYLEL | |
| IL-2 | R & D | 485-MI | |
| DMEM | Invitrogen | 11885 | |
| FBS | HyClone | SH30071.03 | |
| Bovine Serum Albumin | Sigma | A8412 | |
| HEPES | Cellgro | 25-060-Cl | |
| MEM Non-Essential Amino Acids | GIBCO | 11140 | |
| Penicillin/Streptomycin | Gemini | 400-109 | |
| Phenol red-free DMEM | Sigma | D5303 | |
| CO2 Incubator | Thermo Fisher | HeraCell 150i | Kept sterile for cell culture |
| Biological safety cabinet | Thermo Fisher | Forma 1440 | |
| Disposable culture tubes, 6×50 mm Lime Glass | Fisher | 14-958-A | |
| Gamma Counter | Perkin Elmer | Wizard 1470 Automatic Gamma Counter | |
| Confocal microscope | Zeiss | LSM 510 Meta Confocal | With motorized stage and live cell chamber |
| Pipette (1ml, 200μl, 20μl,10μl, 2μl) | Eppendorf | ||
| Tubes (Amber) | Fisher | 50819772 | |
| Centrifuge | Sorvall Legend RT+ | 75004377 | |
| Hemacytometer | Fisher Scientific | 267110 | |
| Upright Microscope | Zeiss | Axioskop40 | |
| NOD.Cg-Rag1tm1Mom Tg(TcraAI4)1Dvs/DvsJ Mice | The Jackson Laboratory | 004347 | |
| NOD.Cg-Rag1tm1Mom Tg(TcrbAI4)1Dvs/DvsJ Mice | The Jackson Laboratory | 004348 | |
| NOD-AI4α/ β F1 mice | N/A | N/A | Bred in UF animal facility |
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